1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a wireless LAN system and a method using the same, and more particularly, to a wireless LAN system and a method using the same, capable of preventing radio interference and crosstalk among different wireless LAN systems located in neighboring areas.
2. Description of the Related Art
The wireless LAN system is used for wireless communications in local areas, and the use of such systems is rapidly spreading due to the widespread presence and use of the Internet, the low-priced wireless devices, the increase of personal information devices, the easy configuration environments, and so on. The wireless LAN system is a communication network in the Industrial Scientific and Medical (ISM) frequency band usable without special license, which helps the spread of wireless LAN systems in homes, school classrooms, and so on.
The standard for a wireless LAN system is defined in detail in the Institute of Electric and Electronics Engineers (IEEE) 802.11 standard. The IEEE 802.11 standard defines four standards such as 802.11, 802.11a, 802.11b, and 802.11 g, as of today, and all the four standards define the use of the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) for path sharing.
The basic building block of a wireless LAN system is a cell which is referred to as a Basic Service Set (BSS) in terms of the 802.11 standard. The cell consists of one or more wireless stations and one Access Point (AP) which is a central base station. Fixed or mobile stations and the central AP communicate with one another, using the wireless Medium Access Control (MAC) protocol of the IEEE 802.11.
FIG. 1 is a view for showing a general structure of a wireless LAN system.
Referring to FIG. 1, one cell 100 is structured with an Access Point AP1 101 and three stations, station 1A 103, station 1B 105, and station 1C 107. The station 1A 103, station 1B 105, and station 1C 107 are connected to a network in a wireless manner, and the Access Point AP1 101 receives and sends out wireless data from the individual stations 103, 105, and 107, to a wired network. The cell 100 of the wireless LAN system is determined by a service space of the Access Point AP1 101 which becomes a service range of the wireless LAN system.
However, the use of such a wireless LAN system has explosively increased, causing a problem of lowering network efficiency due to radio interference among different wireless LAN systems located in neighboring areas. Further, in most occasions, main users and operators of the wireless LAN system are general users having insufficient technical backgrounds, thereby making it difficult for the general users to deal with the technical matters properly.
FIG. 2 is a view for explaining radio interference among wireless LAN systems.
Referring to FIG. 2, there exist four different wireless LAN systems. The first wireless LAN system consists of the Access Point AP1 101), station 1A 103, station 1B 105, and station 1C 107, the second wireless LAN system consists of an Access Point AP2 201, a station 2A 203, a station 2B 205, and a station 2C 207, and the third wireless LAN system consists of an Access Point AP3 301, a station 3A 303, a station 3B 305, and a station 3C 307. Further, the fourth wireless LAN system consists of an Access Point AP4 401, a station 4A 403, a station 4B 405, and a station 4C 407.
In such circumstances, the service range 100 of the first wireless LAN system overlaps with parts of the service range 200 of the second wireless LAN system and the service range 300 of the third wireless LAN system. That is, the station 1C 107 and the station 2A 203 are located in the area where the service range 100 of the first wireless LAN system and the service range 200 of the second wireless LAN system overlap, and the station 1B 105 and the station 3B 305 are located in the area where the service range 100 of the first wireless LAN system and the service range 300 of the third wireless LAN system overlap. In such circumstances, the same channel established and used for the first, second, and third wireless LAN systems produces radio interference and crosstalk, to thereby lower the network efficiency. Further, even though different channels are established for the systems, channels in neighboring frequency ranges also lower the network efficiency.
Table 1 below is one showing ISM band frequency allocations for wireless LAN system by country.
TABLE 1NorthAmericaCenter(USA,Europe,ChannelFrequencyKoreaCanada)AustraliaFranceJapan12412∘∘∘∘22417∘∘∘∘32422∘∘∘∘42427∘∘∘∘52432∘∘∘∘62437∘∘∘∘72442∘∘∘∘82447∘∘∘∘92452∘∘∘∘102457∘∘∘∘∘112462∘∘∘∘∘122467∘∘∘∘132472∘∘∘∘142484∘
The Federal Communication Commission (FCC) recommendation indicates that, in order to avoid interference among wireless LAN systems, a physically stable and independent wireless LAN system without radio interference and crosstalk can be constructed when the center frequency of the current channel established for use is separated by 22 MHz, from the center channel frequency of the channel used by another wireless LAN system, i.e., the current channel is separated by five channels from the channel used by another wireless LAN system. For example, a device using the center channel frequency 2412 MHz on channel 1 would require another device to use the center channel frequency of at least 2434 MHz to avoid interference. From Table 1, the channel which maintains the 22 MHz separation would be 2437 MHz on channel 6. Thus, one channel in use has to be separated by five channels from another channel in use. Accordingly, it is necessary to use a channel separated by more than a certain amount from another channel even though a current channel in use is not the same as a channel in use for another neighboring wireless LAN system.
Therefore, it is necessary to detect whether there is a channel in use of a current wireless LAN system which produces radio interference and crosstalk with a channel in use for another wireless LAN system in a neighboring area, and to properly adjust the current channel in use.